Infrared multiphoton dissociation calculation of a model linear triatomic

Abstract

In a previous paper, we reported preliminary results on the multiphoton dissociation of a linear triatomic molecule. This model consists of a dissociative mode (ν 3) coupled non-linearly to an IR inactive harmonic mode (ν 1). We present here extensive calculations of the dissociation probability as a function of the laser frequency for different pulses of constant fluence. It is shown that dissociation occurs at frequencies either very red-shifted from the ν 3 IR active absorption band or located at the ν 2 and ν 3 bands (due to a 2:1 Fermi resonance). A Hose—Taylor analysis reveals that in the former case excitation proceeds through an anharmonic ladder, while a harmonic one is used in the latter case. In both cases essentially Q states are populated during the excitation process. The dissociation process has been dealt with explicitly by using metastable states to represent the continuum. It is shown that the actual structure of the continuum, due to the presence of Feshbach resonant states, has no real influence on the dissociation probability. Fragment analysis for the ABC → nhw A + BC dissociation process has been performed and shows only a slight departure from statistical distributions, except at very high intensities.